Inhibition of corrosion



ird s 2.89 .12 ITION 0F CORROSION NoDrawing. Application May'31, 1957 Serial No. 662,601

8 Claims. (Cl. 1069-14) The present invention relates to. the prevention of corrosion of metals. by solutions of. organic acid esters of cellulose in halogen-containing organic solvents. More particularly, it relates to novel. processes for preventing such. corrosion. by incorporation inthe solutions ofspecialstabilizing agents.

In the course of converting. organic acidesters. of cellulose, to filamentary material and the like, these esters may be dissolved in halogen-containing organic solvents and. by. way of: illustration, cellulose t-riacetate is dissolved. in methylene chloride which may also contain minor amounts of co-solvents for the ester such as methanol, ethanol, isopropanol or the like, as well as smallamounts of water- This solution or dope is then dry spun into filamentary cellulose, triacetate, the solvent. being evaporated by a currentof wann air followed by recovery and purification prior tov re-use. The spinning;

is effected by passage of the. solution through one or more. orificesina metallic-member in the art. referred to as a jet. It has been found that these jets. as well as. other metal equipment contacted by the solvent during use and recovery corrode rapidly andrequire:v frequent replacement. 7

Itis accordingly an. object. of the present invention. to

minimize or. prevent this corrosion of. metalliemembers contacted by halogen-containing organic solventsfor organic acid esters of cellulose.

It. is afurther object to incorporate in solutions of organic. acid. esters of cellulose. in halogen-containing organic solvents a stabilizer which will inhibitor elimi nate corrosion of iron or steel contacted therewith.

Another. object is, to provide a, solution of cellulose triacetate in methylene chloride, which solution can be dry spun without rapid corrosion of the spinning jet.

Other objects of this inventionwill beapparent from the following detailed description and claims.

In accordance with the present invention, to a halogencontaining organic solvent solution of an organic acid ester of cellulose there is added a stabilizer which in hibits corrosion of metallic members. The stabilizers must satisfy certain requirements in order to be suitable for use, viz., they must themselves be non-corrosive, they should not have any particular afiinity for the cellulose ester lest they contaminate articles produced therefrom, they should not deleteriously affect the physical properties of the cellulose esters, under conditions of use they should not endanger the operators, they should not irritate or sensitize the skin when worn and preferably they should be sufficiently inexpensive so that their cost will be compensated for by savings in the replacement cost of metal equipment or by improvements in the properties of the esters as a result of elimination of metallic contaminants.

The quest for suitable stabilizers is complicated by the fact that the exact mechanism of the corrosion is not fully understood. While it might be expected that the corrosion is the result of the presence of hydrohalic tes Patent acids, stabilizers heretofore used, to. prevent corrosion in other systems or to bind any decomposition products of. halogen-containing. systems, e.g., organometal salts or acid binding agents such as triethylarriine and triethanolamine, are ineifective in the instant situation; Moreover, cororsion' of jets herein involved. is apparently independent of temperature, whereas if the corrosion were the result of decomposition with evolution of hydrogen halide it. would be expected to be' temperature-dependent;

It might also be theorized that the corrosion is due tooxidation but faces of jets exposed to air are even less corroded than those shielded from air. In addition, antioxidants such as. hydroquinone ethers do not exert 'any'appreciable inhibitory effect on solutions of the character herein set forth.

It has. now been found that acetylenic alcohols are effective in avoiding the corrosion of metals by solutions. or organic acid esters of cellulose in halogen-containing organic solvents. Of the acetylenic alcohols, the lower acetylenic alcohols. such as 1,4-butynediol and especially propargyl alcohol (Z-propymL-ol). are. preferred. The. stabilizers will exert some beneficial action even in the smallest amounts but for appreciable inhibition they should be. present in at least. about 0.005% by weight of the. solution. Generally, at least about 0.01% by weightis employed and preferably at least about 0.05%. As much as 0.5% or. even more can be used but since corrosion is substantially completely eliminated with lesser amounts there isrnopoint in adding more stabilizer than is necessary.

The. solvent of the cellulose ester solution can be any halogenated organic. solvent but thepreferred solvents are chlorine-substituted lower alkanes. such as methylene. chloride, .ethylene dichloride, and the like. These may contain. minor amounts of: co-solvents or non-solvents for the esters, dependingupon the properties desired forv the composition and the subsequent treatments towhich. it will be subjected. When a methylene chloride solution is to be used for dry spinning, for example, the methylene chloride solvent may contain as much as 20% by weight of volatile alcohols suchas methanol, ethanol,

propanol isopropanol, and'the like, the percentage being based on the combined weights of methylene chloride and alcohol. Although water Willdecrease the solubility of the ester in the solvent, small amounts can be tolerated. The stabilizing actionwill-berealized even inthe presence of water.

Organic acid esters of cellulose which can be used are preferably the lower alkanoic acid esters such as the acetate, propionate, butyrate, acetate-propionate, acetatebutyrate, and the like. While the invention is applicable to any esters which will dissolve in the indicated solvents, excelleut results are achieved when using a cellulose acetate having an acetyl content in excess of about 59.5% and preferably 61.5% by weight calculated as acetic acid. Such esters are substantially fully acetylated, i.e., free of unreacted hydroxy groups, and are hereinafter referred to as cellulose triacetate although a small residue of unreacted hydroxy groups may be present.

The present invention is particularly useful in the dry spinning of solutions of cellulose triacetate in methylene chloride-methanol such as are disclosed in copending US. application Serial No. 566,088, filed February 17, 1956, by Robert K. Davies and Arnold J. Rosenthal. The solutions there described comprise cellulose acetates having an acetyl value in excess of 59.5% by weight expressed as acetic acid (herein referred to as cellulose triacetate) dissolved in methylene chloride-methanol to a concentration of above 15% and preferably from 17 to 27%. The methylene chloride can range upwards 3 from 80% of thecombined weights of methylene chloride and methanol with about 90% or more preferred. These solutions generally contain small amounts of water, from about 0.3% of the weight of the solution up to the amount which will create turbidityfalthou'gh preferably water is present in no more than 60% by weight of the'amount which will create turbidity. The amount of water which will create turbidity will vary with the composition of the solution. With the minimum concentration of 15% by weight of cellulose triacetate in'the solution and about of methanol in the solvent the turbidity point will correspond to about 1.7% of water.

To prevent corrosion by such solutions, addition of the indicated proportion of propargyl alcohol is especially desirable. During spinning the propargyl alcohol is vaporized along with the solvent and the amount adhered to the cellulose triacetate is extremely small. Any small residual amounts will be removed during the wet treatments to which fabrics made from said filamentary materials are normally subjected.

The following examples are given to illustrate the invention further.

' EXAMPLE I (a) Cellulose acetate having an acetyl value of 59.5% is dissolved in a mixture of 91 parts by weight of methylene chloride and 9 parts by weight of methanol to form a solution having a concentration of cellulose acetate of 21.5% by weight based on the weight of the solution. On spinning this solution at the rate of 100 meters per minute at a temperature of 85 C. through chromium plated stainless steel jets 1 inch in diameter having holes each 0.036 mm. in diameter it is found that the jets corrode and one or more holes thereof become clogged within less than 100 hours. The presence of iron can be detected in the yarn.

(b) By adding 0.05% by weight of propargyl alcohol to the dope, corrosion of new jets does not occur even after 100 hours and jets previously corroded undergo no further corrosion. The physical properties of the filaments are substantially identical with those of filaments spun from the dope of (a) through new jets before appreciable corrosion.

EXAMPLE II To compare the inhibitory action of different concentrations of propargyl alcohol on dopes of varying composition, strips of hot rolled mild steel measuring 7/16 inch by A; inch by 2% inches are immersed in the dopes for 14 days at 50 C. without agitation and the extent of corrosion of the strips is determined. The dopes in this comparison are 15% by weight solutions of cellulose acetate (61.5% acetyl value) in a 91/9 weight mixture of methylene chloride/methanol. Where water or inhibitor is indicated, the percentage is based on the total weight of the dope. The results are shown in the following table:

Table Corrosion Percent Percent Rate Inhibitor Inhibitor Water (Inches x 10* Per Year) None 1.2 20.0 Propargyl 0. 01 1. 4 8, 7 0. 05 1. 3 0. 6 Alcohol 313 3 0. 50 1. 3 0

It is to be understood that the foregoing detailed description is merely given by way of illustration and that many variations may be made therein without departing from the spirit of my invention. V g

A Having described my invention, what I desire to secure by Letters Patent is: V

1. In the process of extruding a 15 to 27% solution of cellulose triacetate in a volatile solvent containing at least.80% of methylene chloride and containing water, in amountvfrom about 0.3% of said solution to the turbidity point, through an opening in a metallic member followed by removal of said solvent, the improvement which comprises incorporating into said solution about 0.005 to 0.5% by weight of an acetylenicalcohol selected from the group consisting of propargyl alcohol and 1,4- butynediol.

2. Process as set forth in claim 1 in'which the solvent contains up to 20% of methanol.

3. Process as set forth in claim 1 in which the acetylenie alcohol is propargyl alcohol and said alcohol is vaporized with said solvent after said extrusion.

4. Process as set forth in claim 1 in which the solution is extruded in filamentary form. I

5. Process as set forth in claim 1 in which said solvent consists essentially of said methylene chloride, said water and methanol.

6. Process as set forth in claim 5 in which the proportion of methanol in said solvent is about 10%.

7. Process as set forth in claim 6 in which the acetylenic alcohol is propargyl alcohol.

8. Process as set forth in claim 7 in which said solutionis extruded in filamentaryform into an evaporative atmosphere.

2,603,622 Berger et al. July 15, 1952 

1. IN THE PROCESS OF EXTRUDING A 15 TO 27% SOLUTION OF CELLULOSE TRIACETATE IN A VOLATILE SOLVENT CONTAINING AT LEAST 80% OF METHYLENE CHLORIDE AND CONTAINING WATER, IN AMOUNT FROM ABOUT 0.3% OF SAID SOLUTION OF THE TURBIDITY POINT, THROUGH AN OPENING IN A METALLIC MEMBER FOLLOWED BY REMOVAL OF SAID SOLVENT, THE IMPROVEMENT WHICH COMPRISES INCORPORATING INTO SAID SOLUTION ABOUT 0.005 TO 0.5% BY WEIGHT OF AN ACETYLENIC ALCOHOL SELECTED FROM THE GROUP CONSISTING OF PROPARGYL ALCOHOL AND 1,4BUTYNEDIOL. 